TY  - JOUR
AU  - Angelopoulos, Panagiotis M.
AU  - Manić, Nebojša
AU  - Janković, Bojan
AU  - Taxiarchou, Maria
PY  - 2022
UR  - https://machinery.mas.bg.ac.rs/handle/123456789/3707
AB  - Thermal decomposition of hydrous volcanic glass occurs through the release of different water species under overlapping processes over wide temperature range. Its investigation is of practical interest since it constitutes integral processing part towards its valorization as source for the production of high-quality porous material for various applications. The study presents investigation of thermal decomposition of hydrous rhyolite through the non-isothermal solid-state kinetics approach. Rhyolite decomposition occurs through three partially overlapping processes, where loosely held and chemically bound water, as well as hydroxyl release at different temperature regions and through different mechanisms. The separation of overlapped thermal curves was done through peak deconvolution method using Frazier-Suzuki equation. Subsequently, the isoconversional (model-free) Friedman, generalized master-plots and Kissinger methods were applied for the determination of apparent activation energy (E-a), reaction model (f(a)) and pre-exponential factor (A) for each individual reaction step considered. Using the kinetic triplet values of each process, the kinetic rate equations were combined allowing precise simulation of the dehydration and dihydroxylation processes. A comparison of model results with thermogravimetric (TG) data, as well as data from the literature, showed the satisfactory accuracy of the model in the simulation of the process and the successful prediction of each water type fraction, during the process evolution. Spectroscopy techniques in UV-VIS and NIR (near infra-red) spectral ranges were applied to raw rhyolite and sample with different water content allowed calculation of color coordinates and its correlation with dehydration and dehydroxylation degrees, and also identification of water species.
PB  - Elsevier, Amsterdam
T2  - Thermochimica Acta
T1  - Thermal decomposition of volcanic glass (rhyolite): Kinetic deconvolution of dehydration and dehydroxylation process
VL  - 707
DO  - 10.1016/j.tca.2021.179082
ER  - 

@article{
author = "Angelopoulos, Panagiotis M. and Manić, Nebojša and Janković, Bojan and Taxiarchou, Maria",
year = "2022",
abstract = "Thermal decomposition of hydrous volcanic glass occurs through the release of different water species under overlapping processes over wide temperature range. Its investigation is of practical interest since it constitutes integral processing part towards its valorization as source for the production of high-quality porous material for various applications. The study presents investigation of thermal decomposition of hydrous rhyolite through the non-isothermal solid-state kinetics approach. Rhyolite decomposition occurs through three partially overlapping processes, where loosely held and chemically bound water, as well as hydroxyl release at different temperature regions and through different mechanisms. The separation of overlapped thermal curves was done through peak deconvolution method using Frazier-Suzuki equation. Subsequently, the isoconversional (model-free) Friedman, generalized master-plots and Kissinger methods were applied for the determination of apparent activation energy (E-a), reaction model (f(a)) and pre-exponential factor (A) for each individual reaction step considered. Using the kinetic triplet values of each process, the kinetic rate equations were combined allowing precise simulation of the dehydration and dihydroxylation processes. A comparison of model results with thermogravimetric (TG) data, as well as data from the literature, showed the satisfactory accuracy of the model in the simulation of the process and the successful prediction of each water type fraction, during the process evolution. Spectroscopy techniques in UV-VIS and NIR (near infra-red) spectral ranges were applied to raw rhyolite and sample with different water content allowed calculation of color coordinates and its correlation with dehydration and dehydroxylation degrees, and also identification of water species.",
publisher = "Elsevier, Amsterdam",
journal = "Thermochimica Acta",
title = "Thermal decomposition of volcanic glass (rhyolite): Kinetic deconvolution of dehydration and dehydroxylation process",
volume = "707",
doi = "10.1016/j.tca.2021.179082"
}

Angelopoulos, P. M., Manić, N., Janković, B.,& Taxiarchou, M.. (2022). Thermal decomposition of volcanic glass (rhyolite): Kinetic deconvolution of dehydration and dehydroxylation process. in Thermochimica Acta
Elsevier, Amsterdam., 707.
https://doi.org/10.1016/j.tca.2021.179082

Angelopoulos PM, Manić N, Janković B, Taxiarchou M. Thermal decomposition of volcanic glass (rhyolite): Kinetic deconvolution of dehydration and dehydroxylation process. in Thermochimica Acta. 2022;707.
doi:10.1016/j.tca.2021.179082 .

Angelopoulos, Panagiotis M., Manić, Nebojša, Janković, Bojan, Taxiarchou, Maria, "Thermal decomposition of volcanic glass (rhyolite): Kinetic deconvolution of dehydration and dehydroxylation process" in Thermochimica Acta, 707 (2022),
https://doi.org/10.1016/j.tca.2021.179082 . .

TY  - JOUR
AU  - Angelopoulos, Panagiotis M.
AU  - Manić, Nebojša
AU  - Tsakiridis, Petros
AU  - Taxiarchou, Maria
AU  - Janković, Bojan
PY  - 2020
UR  - https://machinery.mas.bg.ac.rs/handle/123456789/3409
AB  - Rhyolite is an extrusive, igneous rock of aluminosilicate composition that upon rapid cooling forms obsidian. Obsidian is amorphous and contains limited water portions ( lt  2 mass%); however, secondary hydration turns it either to perlite (H2O approximate to 2-5 mass%) or pitchstone (> 5 mass%). In the current study, kinetics of hydrous rhyolite dehydration were investigated by thermogravimetry up to 1000 degrees C, at heating rates of 2.5, 5, 10 and 20 degrees C min(-1)and under inert atmosphere. The mass loss is approx. 7.6 mass%, occurs along wide temperature range (100-800 degrees C) and is solely attributed to the release of molecular water ((H2O)(m)) and hydroxyl groups (OH). Rhyolite dehydration was considered as a solid-state reaction, and the apparent activation energy (E-a) of dehydration was calculated throughout the whole conversion range (a) by applying the isoconversional Friedman and advanced Vyazovkin methods. Both methods revealed inverse sigmoid trend in E(a)values versus conversion degree, possessing almost stable value of 61 +/- 5 kJ mol(-1)for Friedman method and 59.44 kJ mol(-1)for Vyazovkin method on conversion range between 0.25 and 0.75, and sharp increase at higher conversion degree. The intensive change inE(a)during dehydration progression is attributed to the change in releasing species (from (H2O)(m)to OH). Raman and FT-IR spectroscopy analyses of raw and partially dehydrated samples at different stages revealed that up to 300 degrees C mainly (H2O)(m)is diffused out of the material causing sample enrichment in OH groups. OH release, which occurs at relatively higher temperature, is accompanied by increase in apparent E(a)value of dehydration. Concerning microstructure of raw rhyolite, it exhibits a network of micro-fractures which serve as water release routes. Upon heating, more and wider fractures are created. At 600 degrees C, fractures merging occurs creating voids, which constitute forerunners of the expansion phenomenon. Further temperature increase causes material softening allowing local plastic deformation, which under the high pressure that is exerted by the releasing water species incites the formation of large cavities and fractures, initiating expansion.
PB  - Springer, Dordrecht
T2  - Journal of Thermal Analysis and Calorimetry
T1  - Dehydration of rhyolite: activation energy, water speciation and morphological investigation
EP  - 407
IS  - 1
SP  - 395
VL  - 142
DO  - 10.1007/s10973-020-10105-2
ER  - 

@article{
author = "Angelopoulos, Panagiotis M. and Manić, Nebojša and Tsakiridis, Petros and Taxiarchou, Maria and Janković, Bojan",
year = "2020",
abstract = "Rhyolite is an extrusive, igneous rock of aluminosilicate composition that upon rapid cooling forms obsidian. Obsidian is amorphous and contains limited water portions ( lt  2 mass%); however, secondary hydration turns it either to perlite (H2O approximate to 2-5 mass%) or pitchstone (> 5 mass%). In the current study, kinetics of hydrous rhyolite dehydration were investigated by thermogravimetry up to 1000 degrees C, at heating rates of 2.5, 5, 10 and 20 degrees C min(-1)and under inert atmosphere. The mass loss is approx. 7.6 mass%, occurs along wide temperature range (100-800 degrees C) and is solely attributed to the release of molecular water ((H2O)(m)) and hydroxyl groups (OH). Rhyolite dehydration was considered as a solid-state reaction, and the apparent activation energy (E-a) of dehydration was calculated throughout the whole conversion range (a) by applying the isoconversional Friedman and advanced Vyazovkin methods. Both methods revealed inverse sigmoid trend in E(a)values versus conversion degree, possessing almost stable value of 61 +/- 5 kJ mol(-1)for Friedman method and 59.44 kJ mol(-1)for Vyazovkin method on conversion range between 0.25 and 0.75, and sharp increase at higher conversion degree. The intensive change inE(a)during dehydration progression is attributed to the change in releasing species (from (H2O)(m)to OH). Raman and FT-IR spectroscopy analyses of raw and partially dehydrated samples at different stages revealed that up to 300 degrees C mainly (H2O)(m)is diffused out of the material causing sample enrichment in OH groups. OH release, which occurs at relatively higher temperature, is accompanied by increase in apparent E(a)value of dehydration. Concerning microstructure of raw rhyolite, it exhibits a network of micro-fractures which serve as water release routes. Upon heating, more and wider fractures are created. At 600 degrees C, fractures merging occurs creating voids, which constitute forerunners of the expansion phenomenon. Further temperature increase causes material softening allowing local plastic deformation, which under the high pressure that is exerted by the releasing water species incites the formation of large cavities and fractures, initiating expansion.",
publisher = "Springer, Dordrecht",
journal = "Journal of Thermal Analysis and Calorimetry",
title = "Dehydration of rhyolite: activation energy, water speciation and morphological investigation",
pages = "407-395",
number = "1",
volume = "142",
doi = "10.1007/s10973-020-10105-2"
}

Angelopoulos, P. M., Manić, N., Tsakiridis, P., Taxiarchou, M.,& Janković, B.. (2020). Dehydration of rhyolite: activation energy, water speciation and morphological investigation. in Journal of Thermal Analysis and Calorimetry
Springer, Dordrecht., 142(1), 395-407.
https://doi.org/10.1007/s10973-020-10105-2

Angelopoulos PM, Manić N, Tsakiridis P, Taxiarchou M, Janković B. Dehydration of rhyolite: activation energy, water speciation and morphological investigation. in Journal of Thermal Analysis and Calorimetry. 2020;142(1):395-407.
doi:10.1007/s10973-020-10105-2 .

Angelopoulos, Panagiotis M., Manić, Nebojša, Tsakiridis, Petros, Taxiarchou, Maria, Janković, Bojan, "Dehydration of rhyolite: activation energy, water speciation and morphological investigation" in Journal of Thermal Analysis and Calorimetry, 142, no. 1 (2020):395-407,
https://doi.org/10.1007/s10973-020-10105-2 . .